Re: Unstructured grids

• To: visad-list@xxxxxxxxxxxxx
• Subject: Re: Unstructured grids
• From: "From: Bill Hibbard <hibbard@xxxxxxxxxxxxxxxxx>" <billh@xxxxxxxxxxxxx>
• Date: Tue, 25 May 1999 17:21:11 -0500 (CDT)

Hi Guillaume,

VisAD is intended for any application with numerical data.
Many current applications are in the earth sciences, but
there are also applications in astronomy and textual data
mining (they're described on the VisAD web page).

VisAD support both structured and unstructured grids.
In 3 dimensions, an unstructured grid is constructed by:

  public Irregular3DSet(MathType type, float[][] samples)
                      throws VisADException;

where samples is organized: float[3][number_of_samples].
The Irregular3DSet constructor will implicitly construct
a delaunay tetrahedralization, which can be very slow if
number_of_samples is large.  If the application already
has a topology for the grid, then it can avoid the
delaunay tetrahedralization by using the constructor:

  /** a 3-D irregular set; samples array is organized
      float[3][number_of_samples];  no geometric constraint on
      samples; if delan is non-null it defines the topology of
      samples (which may have manifold dimension 2 or 3), else
      the constructor computes a topology with manifold dimension
      3; note that Gridded3DSet can be used for an irregular set
      with domain dimension 3 and manifold dimension 1;
      coordinate_system and units must be compatible with
      defaults for type, or may be null; errors may be null */
  public Irregular3DSet(MathType type, float[][] samples,
                      CoordinateSystem coord_sys, Unit[] units,
                      ErrorEstimate[] errors, Delaunay delan)
         throws VisADException;

and the constructor:

  public DelaunayCustom(float[][] samples, int[][] tri)
         throws VisADException;

to construct the Delaunay object to pass to Irregular3DSet.
Note tri is organized: int[number_of_tetrahedra][4] - that
is tri[N] is an array of 4 integers, which are the indices
of the 4 vertices of the Nth tetrahedron, in the samples
array.

Note also that you can use Gridded3DSet constructors for
grids that are topologically gridded but curved.

Cheers,
Bill
----------------------------------------------------------
Bill Hibbard, SSEC, 1225 W. Dayton St., Madison, WI  53706
hibbard@xxxxxxxxxxxxxxxxx  608-263-4427  fax: 608-263-6738
http://www.ssec.wisc.edu/~billh/vis.html